1. Field of the Invention
The present invention relates to a manufacturing method for semiconductor devices.
2. Description of Related Art
Semiconductor devices have an STI (shallow trench isolation) structure widely used for isolation between microscopic elements. For the STI structure, associated processes include a step of forming a trench in a surface of a semiconductor substrate, and a step of embedding an insulation film (element isolating insulation film) in the trench. The insulation film embedded in trench may be a film of a silicon oxide, such as silicon dioxide (SiO2), for instance. For formation of the silicon oxide film, there are known processes including, among others, a CVD (chemical vapor deposition) process employing a source gas containing ozone (O3) and TEOS (tetraethoxysilane), HDP (high-density plasma) CVD process, and the like.
Along with miniaturization of semiconductor device, trenches have an increased aspect ratio (trench depth/trench width). It therefore is becoming difficult for the above-noted CVD process or the like to form a silicon oxide film in a trench without producing voids (unfilled part) or seams (joint-like unfilled part). That is, for STI applications, it is getting difficult to make a silicon oxide film with a favorable embedded form.
In this respect, for miniature semiconductor elements from the 100-nm generation, there have been proposals for a process employing a coating type solution SOG (spin-on-grass).
Typically, silicon hydroxide (silanol SiOH4) is dispersed in an organic solvent, such as alcohol, to obtain a solution (silicon hydroxide solution) as an SOG solution to be employed.
This silicon hydroxide solution is applied on a semiconductor substrate, thereby forming a coated film on the semiconductor substrate. After that, the coated film is heated, thereby developing hydrolysis and dehydrating condensation reactions. The coated film is thereby changed to a silicon dioxide film.
Along the course of hydrolysis and dehydrating condensation reactions, significant volume shrinkage develops. As a result, cracks occur in silicon oxide film in the trench. In other words, for STI applications, it is getting difficult to make a silicon dioxide film with a favorable embedded form, even in employment of silicon hydroxide solution.
To this point, among solutions for SOG application, there is a solution containing polysilazane perhydride (polysilazane perhydride solution) that has a relatively small volume shrinkage, which is attracting attention in recent years. Methods being employed include applying the polysilazane perhydride solution on a semiconductor substrate, so as to refill trenches formed in the semiconductor substrate, which is followed by an oxidation treatment in a water vapor atmosphere to thereby form a silicon dioxide film as an element isolating insulation film.
More specifically, polysilazane perhydride ((SiH2NH)n) is dispersed in, among others, xylenen (C6H4(CH3)2) or dibutyl ether ((C4H9)20) or such, thereby forming the polysilazane perhydride solution.
The polysilazane perhydride solution is applied on a surface of a semiconductor substrate, so as to refill trenches formed therein, by a spin coating method (that is the method of spinning a semiconductor substrate, coating with a solution). Resultant coat of polysilazane perhydride solution undergoes a thermal treatment (baking treatment), whereby solvent of polysilazane perhydride solution is volatilized to form a film of polysilazane (referred herein to as “PSZ”). After that, the PSZ film is treated for oxidation to form a silicon dioxide film.
Silicon dioxide films after the oxidation treatment have remaining impurities including, among others, nitrogen (N) contained in the structure of PSZ, and carbon (C) having been contained in a solvent of polysilazane perhydride solution. Such remaining N (nitrogen) and C (carbon) in silicon dioxide film may act as positive bound charges, affecting electrical characteristics and integrity of the semiconductor device.
To this point, there is a technique proposed in Japanese Patent Application Laid-Open Publication No. 2006-222220, in which for a semiconductor substrate formed with a PSZ film and inserted in a diffusion furnace, pressure in the furnace is once dropped, and then water vapor is introduced, thereby raising the furnace pressure, while an oxidation treatment is performed therealong, thereby depriving the PSZ film of impurities such as N (nitrogen) and C (carbon), to change the PSZ film into a silicon dioxide film.
The technique proposed in Japanese Patent Application Laid-Open Publication No. 2006-222220 permits a silicon dioxide film to be formed as an element isolating insulation film with a reduced content of impurities, whereto it has been a desideratum to provide a manufacturing method for semiconductor devices permitting an element isolating insulation film to be formed with the less content of impurity, allowing for unaffected electrical characteristics and integrity.